Hypersensitivity pneumonitis (HP), also called "extrinsic allergic alveolitis," is an immunologically-induced inflammatory disease affecting the alveoli and terminal airways (bronchioles), caused by repeated inhalation of a variety of inciting agents in a susceptible host. A wide range of organic antigens have been identified from different occupations. The clinical presentations of hypersensitivity pneumonitis vary depending upon the frequency, length, and intensity of exposure to the inciting agent. Surprisingly, cigarette smoking reduces the risk of developing the disease due to decreased antibody reaction to the antigen.

00:02
Here we have a really hot topic, called Hypersensitivity
pneumonitis. Clinically called Extrinsic allergicalveolitis. Now, lets go down here for
one second, make sure that you are fullyaware of what’s going on. And by that
I mean, we had a discussion with occupationallung diseases where we looked at pneumoconiosis
and in those, or in that discussion, we lookedat asbestosis, we looked at silicosis, we
looked at berylliosis and we looked at coalworkerpneumoconiosis, didn’t we?Leave that behind and what we have here is
a patient who, once again, is'nt occupation,but in this occupation, does not develop pneumoconiosis.
Does not necessarily develop all the things thatwe talked about earlier, but ends up developing
a “allergic type of issue” and inflammatoryprocess. Now this is a group of mixed
disorder. There’s a lot of research goingon in terms of what exactly is the pathogenesis.
And the one thing that I wish to keep veryclear here is that you do not find
necessarily an abundance of eosinophilia.
01:14
Really? Yeah, you really don't.
01:17
So, at some point, when we jump into our discussion
of eosinophilic pneumonia, hypersensitivitypneumonitis is really not going to be part
of that. Fascinating. So you want to be reallycareful as to how you use the word hypersensitivity
and see as to whether or not... well, yourpatient got exposed to something, is now having
a reaction and maybe a type III/type IV hypersensitivity.
01:41
Type III, immune complex and type IV, your
delayed type of hypersensitivity to environmentalantigens resulting in dyspnoea, cough, chest
tightness and headache. Okay. So, there willbe… the cough, would be more or less your
dry kind of cough, dyspnoea, interstitium isbeing involved. There will be chest tightness
and headache.
02:02
And by environmental antigens, we’re gonna
take a look at the list and this list, aswe go from coast to coast in the United States,
there are a lot of jobs that people have ofall different types and some of these jobs
may include working on the field, workingwith different types of growth in agriculture.
So, our most researched and the most focusedgroup here that we know much about or that
we’re learning to deal, manage these patientsare farmers. And that’s where your focus
should be here as well. What did the farmerthen get exposed to that resulted in Extrinsic
allergic alveolitis? Lets continue.
02:44
Now the antibodies target specific antigens.
So, here is the antigen, environmentally,a protein and even birds. Even pigeons.
Be careful. If you are given a scenario whereyour patient is responsible for, well, we
call them bird fancier, and basically thatmeans that you have an individual that’s
growing birds. Or, while they’re growingbirds though, you think about maybe in their
garage, a very closed environment. Oh, mightystinky. So you walk in here, it smells bad
and it’s not that you’re breathing inCryptococcus neoformans, resulting in a type
of systemic fungal pneumonia. Be careful.
03:26
It’s a fact that, well, if you’re growing
these birds on a regular basis that you mightthen be exposed to the proteins in the wings
or the proteins from the excreta. The proteins,resulting in hypersensitivity pneumonitis.
03:40
Antibodies target specific antigens and approximately
two-thirds of your patients of hypersensitivitypneumonitis develop a non-caseating granuloma.
Yet another example of non-caseating. Youknow about sarcoidosis, you know about Crohn’s
disease, Berylliosis to a certain extent andthen here, hypersensitivity. This is an interstitial
pneumonitis. So therefore what do you thinkyou might have? Increased fibrosis.
And as soon as you have fibrosis that’staking place around the bronchioles, what
may this result in? Once again, bronchiolitisobliterans. You see as to how, that is just
a very generic term or description, but ittells you a lot as to what’s actually taking
place, what exactly is causing the fibrosisin your patient to then obliterate the bronchioles.
04:29
Okay. As I told you earlier, it will be the
farmer that you’re going to be payingattention to. Is that the only patient? No,
but the farmer is going to appear many timeson this table because that’s the focus group
for the most part, in which a patientthen comes in with maybe fever, headache and
chest tightness and coughing. Okay.
04:48
So, if it’s the “farmer’s lung”, exposure
to what? Mouldy hay. And imagine, there israin that has been, you know, going on for
a week and even in the next week, if it’sbeen sunny, you can only imagine that the
hay and as to how it is then mouldy. And thennow the patient has been exposed to Thermophilic
actinomycetes. How does it behave? Behavesas a hypersensitivity pneumonitis. This isn’t
actinomycosis where you end up having thoseyellow-gold and sulphur granules around
the teeth and then may even havea cervicofacial type of fissure. That’s
not what this is. Be careful. Even thoughit seems like it’s the same bacteria, it’s
the particles of proteins.
05:34
What else? We talked about the bird fancier.
These individuals are growing different typesof birds, maybe perhaps even pigeons. But,
look at the antigen that you’ve been exposedto. Proteins and organic dust from the bird
feathers or excreta, not to be confused withCryptococcus neoformans, which will then be
your, well, your caseating typeof granuloma, the type of pneumonia that you’re
probably very, very familiar with. Be careful.
06:02
Next. Byssinosis. So this is the textile
industry. So throughout the entire week,the patient now has been working with cotton,
linen, hemp fibres in which throughoutthe entire week, he or she is breathing this
in and resulting in that chest tightness,headache, not feeling that great. Comes
home on a Friday and tells your, you know,tells your loved one, “Listen, I am not
feeling that great, I don’t feel like goingout. Can we just stay at home and do whatever?”
And then, you see what I’m saying? Hypersensitivitypneumonitis.
06:33
We have others, silo filler’s. You’re
working in a silo, filling stuff up. Whatare you exposed to here in a silo? Fermentation,
nitrogen dioxide. How is your patient goingto present again? Cough. Number 2, it will
be dry in nature, interstitium. Number 2,chest tightness and the most important thing
here is the history of your patient been exposedto whatever antigen that was.
07:00
Then guess what your next step in management
is in all of these cases? Remove the patientfrom the environment to see as to whether or
not the patient is going to be relieved. That’syour next step of management. We’ll talk
more about that coming up.
07:14
Nylon flocker’s. So, those are that are
working with nylon. Proteins from nylon isa big deal.
07:20
And say that you’re working with sugar cane.
This is bagassosis. So, bagassosis would be,if you’re working with sugar cane, then
here, once again, been exposed to Thermophilicactinomyces.
07:31
Now in general, you can see, this is quite
non-specific and vague in terms of symptoms.
07:37
It’s not thoroughly understood, but it’s
understood just enough where we know thatit occurs and the list, ladies and gentlemen,
clinically, I have given you the most commontype of exposures, but it goes by hundreds.
Really. I mean, think about all the differentthings that you might be exposed to.
07:53
Now definition. Here, it is important that
you pay attention. Extrinsic allergic alveolitis.
08:00
How would you diagnose your patient with hypersensitivity
pneumonitis? Now, we’ll walk through thecriteria. So, what we’ll do is, I’m going
to give you the criteria listed below andthen if it’s criteria 1, 2 and 3 that are
met and that’s the one that I want you tofocus upon, then your patient has Hypersensitivity
pneumonitis. The others, well, there’s acombination of others and I’m just gonna…
There it is, take a look at it, but you payattention to 1, 2 and 3.
08:26
Number 1, I told you, history.
As the patient been exposed to whateverantigen in that environment, a farmer, whether
from a silo, was it from birds, so forth.
08:38
Compatible clinical, radiographic and physiologic
findings, what does that mean? On chest X-ray,if it’s the interstitium that’s been affected,
please understand that it will be reticularpattern. Respiratory, well, your constitutional
symptoms there would be your fever, thecough, the chest tightness that we talked
about, the crackles, worsening after severalhours after exposure. That is criteria number
1.
09:03
Criteria number 2. It is not the eosinophilia
that you’re looking for. Is that clear?So even though we call this hypersensitivity
and we even call this allergic, it doesn’tnecessarily mean that you have increased eosinophils.
So what you’re looking for in a BAL, standsfor bronchoalveolar lavage. In the lavage,
you end up finding lymphocytes of a low CD4to CD8 ratio. So, who are you… Which one
of these lymphocytes do you have more of?Good. It’s a CD8. Low CD4 to CD8 ratio.
Criteria number 2. Important.
09:41
Then criteria number 3. Positive inhalation
challenge test. Sure, meaning to say that,now, the patient has been exposed to that
particular antigen and i’ll show you a graphupcoming where it will show you that the symptoms
of your patient is going to worsen.
09:58
If criteria 1, 2 and 3 have been met, then
your patient has hypersensitivity pneumonitis.
10:05
Your first clue that your patient even has
such a pathogenesis or clinical pictureis, number 1, exposure to that antigen, and
number 2, the fever, the dyspnoea, the respiratoryissues and so forth.
10:20
Lets take a look at the graph here and
dissect it with hypersensitivity. And whatthis is, and what it’s going
to show you is the fact thatyou’ll notice that upon exposure, either
to the environment in the natural habitatof your patient or, number two, you’re doing
an antigen type of test that hours later,that you’re going to find worsening
of the patient’s condition. On the X-axisrepresents the time in hours and the Y-axis
represents the percentage change from normalto deteriorating type of condition. The blue
curve represents the environmental challengeand the antigen is in the red curve.
10:59
Okay. So now, I told you, the first criteria
is to see as to whether or not the patient…upon removing the patient from their environment,
are they going to feel better? Well, if fromthe history you keep getting that the patient
says, “Hey, doc, every time I walk in thatsilo, ooh, hours later, I don’t feel very
well, and then I leave and thenI go, you know, take a hot bath or whatever.”
And imagine that, actually that hot bath itselfcould be, you know, another form of hypersensitivity,
but anyhow. They are not gonna give you twoscenarios at the same time. “I feel better
when I remove myself from the environment.”You get that type of history every single
time, that’s your environmental challenge.
11:39
Antigenic challenge is the fact that you are
now, you have to be very careful here though.
11:43
Because if you are going to provide the antigen
which is then going to make the patientfeel not very good, do you understand to as
to how that’s, you know what I mean? Like,exercise caution, make sure that you’re
always properly equipped with any type ofsupportive therapy, just in case, the worst
case scenario. But this is just to illustratethe importance of hypersensitivity pneumonitis
and its importance in terms of exposure.
12:09
Once again, would you tell me as to what that
second criteria was? Good. It was low a CD4to CD8 ratio when dealing with the bronchoalveolar
lavage.

About the Lecture

The lecture Hypersensitivity Pneumonitis (Extrinsic Allergic Alveolitis): Overview and DIagnosis by Carlo Raj, MD is from the course Disorders of the pulmonary circulation and the respiratory regulation.

Included Quiz Questions

All of the following may lead to the development of non-caseating granulomas except which of the following?

Tuberculosis

Sarcoidosis

Extrinsic allergic alveolitis

Crohn’s disease

Berylliosis

What type of hypersensitivity reaction is extrinsic allergic alveolitis?

Mix of delayed cell-mediated and immune complex disease

Immediate allergic reaction

Immune complex mediated

Mix of immune complex and antibody dependent reaction

Cytotoxic, antibody dependent reaction

Which of the following is NOT a common symptom of extrinsic allergic alveolitis?

Productive cough

Chest tightness

Dyspnea

Fever

Headache

Interstitial pneumonitis found in hypersensitivity pneumonitis may progress to fibrosis resulting in which of the following?

Bronchiolitis obliterans

Mesothelioma

Sarcoidosis

Caplan syndrome

Adenocarcinoma of the lungs

What is the first step in the management of a patient with suspected hypersensitivity pneumonitis?

Remove the offending antigen and observe if symptoms remit

Bronchoalveolar lavage

Pulmonary function testing

Corticosteroid therapy

Chest radiograph

The pathophysiology of extrinsic allergic alveolitis involves antibodies, which target specific protein antigens resulting in the development of which of the following?

Non-caseating granulomas

Pleural plaques

Pneumoconiosis

Cavitary lesions

Ferruginous bodies

Which of the following findings would suggest a diagnosis other than hypersensitivity pneumonitis?

Eosinophilia

Periodic symptoms

Positive inhalation challenge test

Non-caseating granuloma on histology

Lymphocyte predominant alveolar sputum sample

All of the following types of extrinsic allergic alveolitis are correctly paired with their etiology EXCEPT which of the following?

Farmer’s lung – actinomycosis

Byssinosis – cotton fiber protein

Nylon flockers lung – nylon fiber protein

Bagassosis – moldy sugar cane

Silo fillers lung – nitrogen dioxide gas

Which of the following would you find on bronchoalveolar lavage of a patient with hypersensitivity pneumonitis?

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